Observations of tJie Transit of Mercury . 195 



berg; the observed times of the flashes to be referred 

 simultaneously to the standard Dent clock of the Ob- 

 servatory and to the chronometers at Helderberg. 

 The programme was as follows : 



Preconcerted Programme of Flash Signals. 



Intervals 



Series. Commencing with between flashes. 



1 May 5th, 8^ 30'" 4 Powder flashes, 5"' 



2 " 5th, 21'' 00 20 Heliotrope flashes, 1'" 



3 " 6th, 8'' 30 4 Powder flashes, 5'" 



[i^.] Sextant solar and star observations to be used in con- 

 junction with or in case of failure of [A}. 



[C] The chronometers of the expedition, transported with 

 great care, but to be relied on only In case of failure of 

 both [A] and [5]. 



The difficulty experienced in obtaining a sufficient num- 

 ber of good sextant observations owing to the interference 

 of clouds, together with the fact that the present imperfect 

 working condition of the instrument necessitated the use of 

 a small weight for the results, have led me to depend alone 

 on the flash signals for the adopted time, though the results 

 of the sextant work are here given : 



Sextant Observations. Altitudes of Sun. 



No. of Chronometer 

 Date. contacts. Correction to Held, M. T. Observer. 



May 5d.85, 1st Series, 10 — 1'» 2^26 Wilson 



" 5 .86, 2d Series 10 —1 1 .60 — 1^ l.s^s 



6. 19 2 —1 11 .38 



Mean correction to Helderberg M. T., — 1'" 6.65 



Longitude correction to Dudley Observatory ^-l^ 



May 6.(^03 Chronometer correction to D. 0. M. T., — 0'" 3.^55 



